1. Field of the Invention
The present invention relates to a lens retaining barrel which is capable of retaining a lens so that the axis of the barrel is coincident with the optical axis of the lens.
2. Description of the Related Arts
Recently plastic molded parts have been used as lens retaining barrels to a considerable extent. FIG. 17 shows a conventional lens retaining barrel 100 which is molded out of plastic and includes a cylindrical part 101 into which a lens L is fitted and an abutment 102 provided inside the cylindrical part 101.
The cylindrical part 101 is adapted to be in contact with the lens outer periphery to position the lens L in the radial direction, while the abutment 102 is brought into contact with the lens L inserted into the cylindrical part 101 to thereby position the lens L in the direction of the optical axis thereof. The lens L inserted into the cylindrical part 101 is rigidly retained within the lens retaining barrel by means of adhesive or caulking.
A mold for molding such a lens retaining barrel 100 can be assembled by inserting an insert into a matrix. The outside part of the lens retaining barrel 100 is molded with the matrix while the inside part of the lens retaining barrel 100 is molded with the insert. In other words, the inner surface of the cylindrical part 101 and the abutment 102 are to be molded with the aid of the insert. When molding by the use of such mold, close attention has to be paid to the shapes and thickness of mold components and, the position of a resin injection gate so as not to cause a deformation in the lens retaining barrel, that is, so as not to bring about an eccentricity or tilt of the lens at the time of mounting the lens.
However, in spite of the closest attention on molding and an enhanced accuracy of the mold such as the insert, it is difficult to entirely eliminate the deformation of the lens retaining barrel to be molded. When a lens requiring a higher centering accuracy is mounted into such barrel, the deformation often causes the reduction in the mounting accuracy. The concrete causes are supposed to be based on the following two items.
(1) Eccentricity of Lens
The inner surface (lens fitting portion) of the cylindrical part 101 into which the outer periphery of the lens L is fitted is deformed, and the center of the inscribed circle of the lens fitting portion is deviated from the optical axis of the lens L. This causes an eccentricity of distance .delta. as shown in FIG. 17a.
(2) Tilt of Lens
A receiving surface of the abutment 102 in the direction of the optical axis is not allowed to be orthogonal to the optical axis of the lens due to the deformation. As a result, the lens is tilted by angles .epsilon..sub.1, .epsilon..sub.2 as shown in FIG. 17b.
In order to cope with the above two causes, conventionally the diameter of the lens fitting portion, that is, the outer diameter of the insert, was set somewhat larger in view of the eccentricity of the lens fitting portion, and troublesome assembling works were needed such as adjusting the abutting condition of the abutment against the receiving surface at the time of mounting the lens, which requires considerable practice.
The present invention was conceived in view of the above problems, and aims to provide a lens retaining barrel free from any eccentricity or tilt of the lens and having a higher mounting accuracy and being easy to assemble for mounting.